Ron Sider, in If Jesus is Lord, reduces it to five crucial theological foundations:

Incarnation, resurrection, inauguration of the kingdom, anti-world, and the importance of the church.

Biblical pacifism rests on several central theological affirmations. If the historic creeds are correct that Jesus is truly God and truly human, then rejecting Jesus’s teaching on loving enemies involves fundamental christological heresy.

Only if Jesus rose bodily from the dead does it make sense to claim that we should still believe that his messianic kingdom has truly begun and his followers should and can live the ethics of his dawning kingdom.

It is true that the New Testament teaches that Christ’s kingdom is not yet here in its fullness. But nowhere does the New Testament conclude that therefore Christians should postpone living Jesus’s kingdom ethics until the returning Christ brings the completion of the kingdom.

On the contrary, the New Testament repeatedly insists that Christians should not be conformed to the patterns of the fallen world (Rom. 12:1-2).

To do that, to be sure, we need the loving support of the church, Jesus’s new messianic community. Lacking that communal support and the empowering presence of the Holy Spirit. non-Christians will frequently not succeed in living Jesus’s ethic, including his call to love enemies. But they should.